Under water acoustics plasma generator

ABSTRACT

A system and method for evaluating a bond is provided. The system uses an underwater spark discharge to generate a compression wave in a first vessel containing a liquid. The system further includes a second vessel in which a vacuum is pulled to hold the first vessel against a bonded structure being inspected. The compression wave is directed to propagate from the liquid into the bonded structure to apply a known force to the bond being inspected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 63/125,790, filed on Dec. 15, 2020, the entirety of which is incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure is directed to systems and methods for evaluating a bond between two components. More particularly, the present disclosure is directed to systems and methods for evaluating a bond between two components using an underwater spark discharge to generate a compression wave.

BACKGROUND

Laser bond inspection (LBI) is an inspection method that can be used to evaluate the quality of adhesive bonds in a structure. During laser bond inspection, a plasma is created by using a laser pulse to ablate a sacrificial layer to generate compression waves in the structure. The structure can be, for example, a composite structure including a carbon fiber reinforced polymer (CFRP)-to-CFRP bond or CFRP-to-metal bond. The compression wave mechanically creates a stress load on the adhesive bond. During exposure to this load, a weak bond will fail, and a strong bond will not. Structures with weak bonds are thus identified and repaired or discarded. However, current LBI systems require lasers and power supplies that are large and expensive. Therefore, an improved system and method for evaluating a bond that eliminates the laser is desired.

SUMMARY

A system for evaluating a bond is disclosed. The system includes a first vessel having one or more sidewalls and an endwall, a liquid port configured to connect to a source to fill the first vessel with a liquid, and an open portion configured to be placed against a bonded structure to be inspected. The system also includes a second vessel surrounding the open portion of the first vessel, having a vacuum port configured to connect to a vacuum system to pull a vacuum in a space between an outer surface of the first vessel and an inner surface of the second vessel when the open portion of the first vessel and an open portion of the second vessel are adjacent to the bonded structure to be inspected. The system further includes a pair of electrodes disposed within the first vessel and a power supply connected to the pair of electrodes, wherein the power supply is configured to provide an electrical pulse to create an underwater plasma between the pair of electrodes to generate a compression wave.

A method for evaluating a bond is also disclosed. The method includes placing an open portion of a first vessel against a bonded structure being inspected, pulling a vacuum between an outer surface of the first vessel and an inner surface of a second vessel that encloses the first vessel, wherein pulling the vacuum seals the first vessel to the bonded structure, and filling the first vessel with a liquid, wherein the liquid contacts a surface of the bonded structure to be inspected at the open portion. The method also includes initiating a spark discharge in the liquid to form a plasma that generates a compression wave in the liquid, wherein the compression wave propagates from the liquid into the bonded structure through the open portion to apply a force to a bond in the bonded structure. The method further includes inspecting the bond in the bonded structure.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate aspects of the present teachings and together with the description, serve to explain the principles of the present teachings.

FIG. 1A schematically illustrates a cross-sectional view of a system for evaluating an adhesive bond in a bonded structure, according to an implementation.

FIG. 1B schematically illustrates an end view of a system for evaluating a bond in an bonded structure, according to another implementation.

FIG. 1C schematically illustrates a side view of a system for evaluating a bond in an bonded structure having a curved surface, according to another implementation.

FIG. 1D is a functional block diagram of a system for evaluating an adhesive bond in a bonded structure, according to an implementation.

FIG. 2 schematically illustrates a cross-sectional view of a system for evaluating an adhesive bond in a bonded structure, according to another implementation.

FIG. 3 is a flowchart of a method for evaluating a bond in a bonded structure, according to an implementation.

FIG. 4 schematically illustrates a cross sectional view of a system for evaluating a bond in a bonded structure, according to an implementation.

It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding rather than to maintain strict structural accuracy, detail, and scale.

DESCRIPTION

Reference will now be made in detail to the present teachings, examples of which are illustrated in the accompanying drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific examples of practicing the present teachings. The following description is, therefore, merely exemplary.

The present disclosure is directed to an inspection system and method that uses an underwater plasma to generate a compression wave to evaluate a strength of bonding parameters between two adjacent layers in a structure. Compression waves are also referred to herein as stress waves or longitudinal waves. The inspection system includes a first vessel containing a liquid in which an underwater plasma generates a compression wave. The compression wave propagates from the liquid into the structure to mechanically stress the bond, as described in greater detail below. While the compression wave stresses the bond in a manner similar to LBI, the disclosed inspection system and method using the underwater plasma eliminates the need for a laser and its power supply required for LBI thereby reducing the size and cost of the equipment for bond inspection. The reduced size further provides increased portability to allow easier and more efficient inspection of a greater range of shapes and sizes of bonded structures compared to, for example, ASTM Standard D5868—Lap Shear Adhesion for Fiber Reinforced Plastic (FRP) Bonding, ASTM Standard D1002—Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded, and ASTM Standard D3167—Standard Test Method for Floating Roller Peel Resistance of Adhesives.

FIGS. 1A-B illustrate schematic views of a system 100 for evaluating a bond in a bonded structure, according to an implementation. As shown in the cross-sectional schematic view of FIG. 1A, system 100 includes a first vessel 110 having an endwall 112, one or more sidewalls 114, and an open portion 130 opposite endwall 112. Open portion 130 can be an entire wall (e.g., an endwall) opposite endwall 112 or be a portion of the wall opposite endwall 112. First vessel 110 further includes a liquid port 120 that can be used to fill the first vessel with a liquid when connected to a source of liquid. As will be discussed in more detail below, first vessel 110 functions to contain the liquid and open portion 130 allows the liquid to contact a bonded structure to be inspected. A bonded structure 190 shown in FIG. 1A can be, for example, a structure formed by a first component and a second component that are bonded together by a bond as described in more detail below.

System 100 also includes a second vessel 140 having one or more sidewalls 144, an endwall 142, an open portion 150, and a vacuum port 170 that can be connected to a vacuum system. Second vessel 140 surrounds open portion 130 of first vessel 110, and may completely enclose first vessel 110 as shown in FIG. 1A. This allows a vacuum to be pulled in a space 160 between an outer surface of first vessel 110 and an inner surface of second vessel 140 when system 100 is placed in contact with a bonded structure 190 to be inspected.

FIG. 1B shows an end view of system 100, specifically the end including the open portions that contact the bonded structure to be inspected. During inspection, the bonded structure is placed over open portion 130 of first vessel 110 and open portion 150 of second vessel 140. First vessel 110 is filled with the liquid through liquid port 120 and a vacuum is pulled within space 160 via vacuum port 170. To keep the liquid within first vessel 110 from leaking and to facilitate establishing a vacuum in space 160, a seal 119 can optionally be included at an end of sidewall 114 adjacent to open portion 130 of first vessel 110. Similarly, a seal 149 can optionally be included at an end of sidewalls 144 adjacent to open portion 150 of second vessel 140. Although depicted as cylindrical in shape, one of ordinary skill in the art will understand that other shapes can be used, in particular, shapes that focus the compression wave towards the structure being inspected.

End of sidewall 114 at open portion 130 is depicted as planar to allow inspection of a bond within bonded structure 190 having a flat surface. A structure being inspected having a curved or shaped surface can be inspected by conforming ends of sidewalls of first vessel 110 and second vessel 140 to have a shape or curvature that matches a shape or curvature of the surface of the structure being inspected. As shown in FIG. 1C, a bonded structure 196 can have a surface 197 that is shaped or curved and an end of sidewall 144 of second vessel 140 can have a shape or curvature that matches the shape or curvature of surface 197 of bonded structure 196. Similarly, an end of sidewall 114 of first vessel 110 can have a shape or curvature that matches a shape or curvature of surface 197 of the bonded structure 196 being inspected. Ends of the sidewalls that match the shape or curvature of the surface of the structure being inspected allows first vessel 110 to be filled with the liquid without leakage and allows the vacuum to be pulled in space 160 between first vessel 110 and second vessel 140. This can optionally be accomplished by seals 119 and 149 having a curvature and/or shape to match the shape or curvature of the surface of the structure being inspected. One of ordinary skill in the art will understand that surface 197 that is shaped or curved may affect propagation of the compressive wave from the liquid in first vessel 110 into bonded structure 196 and that the pulse amplitude and/or pulse width of the compressive wave may need to be adjusted.

System 100 further includes a pair of electrodes 180 disposed in first vessel 110 and a power supply 185 connected to pair of electrodes 180. As used herein, pair of electrodes refers to an anode and a cathode separated by a gap. Pair of electrodes 180 can be, for example, part of a spark plug, e.g., a spark plug for a combustion engine. Pair of electrodes 180 are positioned so that the compression wave generated in the liquid can propagate towards the structure being inspected. For example, pair of electrodes 180 can be positioned in front of open portion 130 of first vessel 110 so that the compression wave can propagate through open portion 130 into the structure being inspected. Power supply 185 supplies an electrical pulse to initiate the spark discharge at electrodes 180. The electrical pulse generates a compression wave with high amplitude and short pulse width for bond inspection, for example, high amplitude and short pulse comparable to a compression wave generated by an LBI system. Power supply 185 can provide about 40 kV to about 60 kV to pair of electrodes 180 and can be, for example, one or more banks of capacitors. The one or more banks of capacitors can be variable capacitors including time delay capability. Power supply 185 can also provide a voltage (e.g., and electrical pulse) via a transformer to produce arcing at pair of electrodes 180 at a desired voltage. Examples of transformers include, but are not limited to, an oscillator transformer and flyback transformer. Power supply 185 can also be a Van de Graaff belt high voltage electrostatic generator or other sources of an electrical pulse.

FIG. 1D is a function block diagram of an example system 100 for evaluating a bond in a bonded structure using underwater spark discharge. System 100 is placed adjacent to bonded structure 190. A vacuum system 177 can pull a vacuum in space 160 in second vessel 140 via vacuum port 170. The vacuum secures system 100 against a surface of bonded structure 190 and seals 147 prevent loss of vacuum from space 160. A source of liquid 128 can fill first vessel 110 with a liquid via liquid port 140. Seals 147 can prevent the liquid from leaking out of first vessel 110 to avoid the presence of an air gap/pocket in first vessel 110 that could affect propagation of the compressive wave into bonded structure 190. Power supply 185 can provide an electrical pulse to pair of electrodes 185 that results in a spark discharge that generates a plasma between pair of electrodes 185. The spark discharge generates a compression wave that propagates from the liquid into bonded structure 190 to apply a force to the bond. Subsequent to applying the force to the bond, source of liquid 128 can remove the liquid from first vessel 110 and vacuum system 178 can remove the vacuum from second vessel 140 to release the system from bonded structure 190.

FIG. 2 illustrates a cross-sectional view of a system 200 for evaluating a bond in a bonded structure in which a first vessel and a second vessel share common sidewalls and/or a common endwall, according to another implementation. System 200 includes a second vessel 240 having one or more sidewalls 244, an endwall 242, and an open portion 250 opposite endwall 242. Second vessel 240 also includes a vacuum port 270 that can pull a vacuum in space 260 when connected to a vacuum system. System 200 also includes a first vessel 210 having an endwall 242, one or more sidewalls 214, 244, and an open portion 230 that is opposite endwall 242. First vessel 210 further includes a liquid port 220 that can fill the first vessel with a liquid when connected to a source of liquid. First vessel 210 can optionally include an air vent 223 to remove air, for example in the form of bubbles, when first vessel 210 is filled with the liquid.

As shown in FIG. 2, second vessel 240 and first vessel 210 share endwall 242. Second vessel 240 also shares a portion of sidewall 244 with first vessel 210. In other words, endwall 242 functions as an endwall for both first vessel 210 and second vessel 240. Similarly, sidewall 244 functions as a sidewall for second vessel 240 and a portion of sidewall 244 also functions as a side wall for first vessel 210.

During inspection, a bonded structure is placed over open portion 230 of first vessel 210 and open portion 250 of second vessel 240. First vessel 210 is filled with the liquid through liquid port 220 and a vacuum is pulled within space 260 via vacuum port 270. Seals optionally located at the ends of the sidewalls that contact the bonded structure can keep the liquid within first vessel 210 from escaping and facilitate establishing a vacuum in space 260. Pair of electrodes 280, for example, part of a spark plug, immersed in the liquid are provided with an electrical pulse from a power supply 285. The electrical arc formed between pair of electrodes 280 generates a plasma within the liquid that in turn generates a compression wave directed towards the bonded structure through open portion 230 of first vessel 210.

FIG. 3 is a flowchart illustrating a method for 300 for evaluating a bond in a structure, according to an implementation.

At 310 of method 300, a system for evaluating a bond as disclosed herein can be placed against a structure to be inspected. Referring to FIG. 4 that schematically illustrates operation of a system as disclosed herein, a system 400 for evaluating a bond can be placed against a structure 490 being inspected. Structure 490 can be, for example, a structure formed by a first component 492 and a second component 494 that are bonded together by a bond 493. First component 492 and second component 494 can be, for example, layers within a composite structure. As will be appreciated, there may be more components that are bonded together, but for simplicity, only two components are illustrated. In some examples, first component 492 and second components 494 are made at least partially from CFRP. In other examples, first component 492 is made at least partially from CFRP, and second component 494 is made at least partially from metal. Bond 493 can include a bond material such as a resin, an adhesive, or an epoxy (e.g., boron epoxy or carbon epoxy).

System 400 is placed against structure 490 so that open portions of a first vessel 410 and a second vessel 440 are closed by structure 490. In other words, structure 490 closes open portions of first vessel 410 to allow liquid to fill first vessel 410 and to contact a surface of structure 490. Structure 490 also closes open portions of second vessel 440 to allow a vacuum to be pulled in second vessel 440, for example, in space 460 between the inside of a sidewall of second vessel 440 and an outside of a sidewall of first vessel 410.

At 320 of method 300, a vacuum is pulled within second vessel 440. Referring to FIG. 4, the vacuum is pulled in space 460 of second vessel 440 via a vacuum port 470 connected to a vacuum system. The vacuum holds first vessel 410 and second vessel 440 against structure 490 to create a watertight chamber within first vessel 410 and to keep system 400 from moving during inspection, for example, when a compression wave is generated. The vacuum also enables system 400 to be placed in various orientations where system 400 may held against structure 490 by the vacuum, for example, where structure 490 includes a vertical or angled surface to be inspected. Seals, sealant materials, or gaskets can be disposed between ends of the sidewalls adjacent to the open portions and structure 490 to assist pulling and retaining the vacuum and/or to prevent leakage of the liquid. The vacuum further allows system 400 to be placed with open portion of first vessel 410 at various orientations, such as facing up as shown in FIGS. 1A and 2, facing down as shown in FIG. 4, or facing sideways at any angle.

At 330 of method 300, the first vessel is filled with a liquid. Referring to FIG. 4, first vessel 410 is filled with a liquid 425 via a liquid port 420 connected to a source of liquid. Liquid 425 can be water, for example, deionized water, or an oil, such as a mineral oil or a nonconductive oil. Liquid 425 serves as a medium to generate and propagate a compression wave generated by the underwater spark discharge. First vessel 410 can optionally be filled with the liquid to a pressure up to about 100 psi, for example from about 5 to about 90 psi, or from about 10 to about 75 psi. The pressure within first vessel 410 can increase an amplitude of the compression wave generated at 340 of method 300 below. System 400 can also optionally include additional liquid ports, for example, a second liquid port 421 to increase the speed of filling and emptying vessel 410 and/or to prevent contamination of the source of liquid due to breakdown of the liquid by the plasma. System 400 can also optionally include an air vent 423 configured allow removal of air, for example, air bubbles, from vessel 410. Valves capable of withstanding the stress wave generated by system 400 can be used to close off system 400 at air vent 423, liquid ports 420, 412, and/or vacuum port 470. Examples of suitable valves include, but are not limited to, actuated valves and mechanical valves.

At 340 of method 300, an electrical pulse is transmitted to a pair of electrodes that are immersed in the liquid in first vessel 410 to initiate a spark discharge. Referring again to FIG. 4, a pair of electrodes 480 is immersed in liquid 425 within first vessel 410. Pair of electrodes 480 can be, for example, part of a conventional spark plug for a combustion engine. In other implementations, the pair of electrodes can be replaced or modified to generate different pulse widths, electrical arcs with different properties, stress waves with different properties, or a combination thereof. For example, one or both of the electrodes of the pair of electrodes can be replaced with different electrode(s) that are made of a different material and/or have a different size/shape. In addition, the positioning of the electrodes, for example, a gap length between the electrodes can be varied to alter and/or control the plasma. For example, the gap length between the pair of electrodes and/or the liquid density can selected or modified to control the spark discharge which affects parameters of the compression wave, for example, its pulse width, frequency, and power (dB).

The electrical pulse is provided by a power supply 485, for example, a bank of capacitors, a voltage induction source, or voltage switching source, provides a voltage capable of forming an underwater plasma that generates a high amplitude, short wavelength compression wave for bond inspection. The high amplitude, short wavelength compression wave can have a pulse width of about 100 ns to about 300 ns and an energy of about 5 to about 40 Joules. The high amplitude, short wavelength compression wave can further be comparable to a compression wave generated during LBI inspection. Power supply 485 can provide about 40 kV to about 60 kV to pair of electrodes 480 to generate the underwater plasma and the resulting compression wave having a duration or pulse width of about 100 ns to about 300 ns and an energy of about 5 to about 40 Joules.

Although not wishing to be bound by any particular theory, it is believed that the electrical pulse when transferred to the pair of electrodes causes a high intensity electric field across the gap of the pair of electrodes within the liquid. This results in ionization of the liquid molecules and formation of a gaseous plasma. High temperature and pressure generated by the plasma and opposed by the liquid, results in an acoustic wave, e.g., a compression wave, that propagates outwards with an amplitude sufficient to change the density of the liquid.

The compression wave generated in liquid 425 by the plasma propagates through the liquid and into first component 492 of structure 490. The compression wave propagates through first component 492 and applies a force to bond 493. In various implementations, the force needed to damage or break a bond with a satisfactory/passing quality may be known prior to performing the disclosed method. Thus, the force can be a predetermined force, for example, from about 30% to about 70% (e.g., about 50%) of the force required to break bond 493, in a manner similar to adhesive bond testing by LBI or peel ply. The predetermined force applied by the compression wave is controlled by, for example, the length of the gap between the electrodes, the size and width of electrical pulse, and size and shape of the first vessel, and/or the liquid in the vessel. A force can further be applied to bond 493 from a reflected compression wave after the compression wave is reflected from a surface of first component 492, a surface of second component 494, and/or bond 493. The predetermined force can be based on, for example, peel ply testing in a manner similar to establishing a predetermined force in laser bond inspection.

At 340 of method 300, the bond can be inspected. For example, bond 493 can be inspected with a non-destructive inspection (NDI) system including but not limited to an ultrasound imaging system or an ultrasonic inspection system. The inspection detects inconsistencies and/or damage to the bond that occurs in response to the compression wave and/or a reflected compression wave reflected from a back surface of the structure. If the inspection reveals that bond 493 is fractured or broken, then the quality of the bond is determined to be bad (i.e., the bond did not pass inspection). If the inspection reveals that bond 493 (e.g., material forming the bond) is not fractured or broken, then the quality of the bond is determined to be good (i.e., the bond passes inspection). Such an inspection of the bond is comparable to inspection by LBI and ASTM D5528-13—Standard Test Method for Mode 1 Interlaminar Fracture Toughness of Unidirectional Fiber-reinforced Polymer matrix composites. Alternative or additional steps may also be performed.

The disclosed system and method can replace destructive testing such as peel ply tests, which use mechanically applied stress to pull a bond apart. The disclosed system and method can also replace LBI tests, which use an expensive and large laser/power supply and further requires a sacrificial material for ablation to generate a compression wave.

Further, the disclosure comprises examples according to the following clauses:

Clause 1. A system for evaluating a bond comprising: a first vessel comprising, one or more sidewalls and an endwall, a liquid port configured to connect to a source to fill the first vessel with a liquid, and an open portion configured to be placed against a bonded structure to be inspected; a second vessel surrounding the open portion of the first vessel, comprising a vacuum port configured to connect to a vacuum system to pull a vacuum in a space between an outer surface of the first vessel and an inner surface of the second vessel when the open portion of the first vessel and an open portion of the second vessel are adjacent to the bonded structure to be inspected; a pair of electrodes disposed within the first vessel; and a power supply connected to the pair of electrodes, wherein the power supply is configured to provide an electrical pulse to create an underwater plasma between the pair of electrodes to generate a compression wave

Clause 2. The system of any of Clauses 1 or 3-9, further comprising one or more seals configured to seal the first vessel against the structure when the vacuum is pulled in the space between the outer surface of the first vessel and the inner surface of the second vessel.

Clause 3. The system of any of Clauses 1, 2 or 4-9, further comprising a spark plug that comprises the pair of electrodes.

Clause 4. The system of any of Clauses 1-3 or 5-9, wherein the power supply provides about 40 kV to about 60 kV to the pair of electrodes.

Clause 5. The system of any of Clauses 1-4 or 6-9, wherein the pair of electrodes comprise a gap that discharges a spark to generate a compression wave with a pulse width of about 100 ns to about 300 ns and an energy of about 5 to about 40 Joules per pulse.

Clause 6. The system of any of Clauses 1-5 or 7-9, wherein the liquid port is configured to connect to a source of water, deionized water, mineral oil, or a non-conductive fluid.

Clause 7. The system of any of Clauses 1-6 or 8-9, further comprising an additional liquid port and/or an air vent.

Clause 8. The system of any of Clauses 1-7 or 9, wherein the first vessel and the second vessel comprise an endwall and/or a sidewall that is common to both the first vessel and the second vessel.

Clause 9. The system of any of Clauses 1-8, wherein an end of the one or more sidewalls of the first vessel comprise a shape and/or curvature that matches a shape and/or curvature of a surface of the structure to be inspected.

Clause 10. A method for evaluating a bond, comprising: placing an open portion of a first vessel against a bonded structure being inspected; pulling a vacuum between an outer surface of the first vessel and an inner surface of a second vessel that encloses the first vessel, wherein pulling the vacuum seals the first vessel to the bonded structure; filling the first vessel with a liquid, wherein the liquid contacts a surface of the bonded structure to be inspected at the open portion; initiating a spark discharge in the liquid to form a plasma that generates a compression wave in the liquid, wherein the compression wave propagates from the liquid into the bonded structure through the open portion to apply a force to a bond in the bonded structure; and inspecting the bond in the bonded structure.

Clause 11. The method for evaluating a bond of any of Clauses 10 or 12-20, wherein the bond in the bonded structure comprises a metal-to-composite adhesive bond or a composite-to-composite adhesive bond.

Clause 12. The method for evaluating a bond of any of Clauses 10, 11 or 13-20, wherein pulling the vacuum between the outer surface of the first vessel and the inner surface of a second vessel comprises compressing seals disposed between the first vessel and the bonded structure and compressing seals disposed between the second vessel and the bonded structure.

Clause 13. The method for evaluating a bond of any of Clauses 10-12 or 14-20, wherein filling the first vessel with a liquid comprises filling the first vessel with water or oil.

Clause 14. The method for evaluating a bond of any of Clauses 10-13 or 15-20, wherein filling the first vessel with the liquid comprises introducing a pressure of up to about 100 psi in the first vessel.

Clause 15. The method for evaluating a bond of any of Clauses 10-14 or 16-20, wherein initiating the spark discharge in the liquid comprises supplying about 40 kV to about 60 kV to a pair of electrodes disposed in the first vessel.

Clause 16. The method for evaluating a bond of any of Clauses 10-15 or 17-20, wherein initiating the spark discharge in the liquid to form the plasma generates a compression wave in the liquid having a pulse width of about 100 ns to about 300 ns.

Clause 17. The method for evaluating a bond of any of Clauses 10-16 or 18-20, wherein initiating a spark discharge in the liquid comprises providing an electrical pulse from a bank of capacitors to a spark plug.

Clause 18. The method for evaluating a bond of any of Clauses 10-17 or 19-20, wherein the force applied to the bond by the compression wave is from about 30% to about 70% of a force required to break the bond.

Clause 19. The method for evaluating a bond of any of Clauses 10-18 or 20, further comprising applying another force to the bond by a reflected compression wave.

Clause 20. The method for evaluating a bond of any of Clauses 10-19, wherein inspecting the bond in the bonded structure comprises using ultrasound to inspect the bond.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein.

While the present teachings have been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the present teachings may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function. As used herein, the terms “a”, “an”, and “the” may refer to one or more elements or parts of elements. As used herein, the terms “first” and “second” may refer to two different elements or parts of elements. As used herein, the term “at least one of A and B” with respect to a listing of items such as, for example, A and B, means A alone, B alone, or A and B. Those skilled in the art will recognize that these and other variations are possible. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” Further, in the discussion and claims herein, the term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the intended purpose described herein. Finally, “exemplary” indicates the description is used as an example, rather than implying that it is an ideal.

It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompasses by the following claims. 

What is claimed is:
 1. A system for evaluating a bond comprising: a first vessel comprising, one or more sidewalls and an endwall, a liquid port configured to connect to a source to fill the first vessel with a liquid, and an open portion configured to be placed against a bonded structure to be inspected; a second vessel surrounding the open portion of the first vessel, comprising a vacuum port configured to connect to a vacuum system to pull a vacuum in a space between an outer surface of the first vessel and an inner surface of the second vessel when the open portion of the first vessel and an open portion of the second vessel are adjacent to the bonded structure to be inspected; a pair of electrodes disposed within the first vessel; and a power supply connected to the pair of electrodes, wherein the power supply is configured to provide an electrical pulse to create an underwater plasma between the pair of electrodes to generate a compression wave.
 2. The system of claim 1, further comprising one or more seals configured to seal the first vessel against the structure when the vacuum is pulled in the space between the outer surface of the first vessel and the inner surface of the second vessel.
 3. The system of claim 1, wherein the pair of electrodes comprises an anode and a cathode separated by a gap length, and wherein the electrical pulse provided by the power supply bridges the liquid between the gap length to generate the underwater plasma.
 4. The system of claim 1, wherein the power supply provides about 40 kV to about 60 kV to the pair of electrodes.
 5. The system of claim 3, wherein the gap length is configured to generate a compression wave with a pulse width of about 100 ns to about 300 ns and an energy of about 5 to about 40 Joules.
 6. The system of claim 1, wherein the liquid port is configured to connect to a source of water, deionized water, mineral oil, or a non-conductive fluid.
 7. The system of claim 1, further comprising an additional liquid port and/or an air vent.
 8. The system of claim 1, wherein the first vessel and the second vessel comprise an endwall and/or a sidewall that is common to both the first vessel and the second vessel.
 9. The system of claim 1, wherein an end of the one or more sidewalls of the first vessel comprise a shape and/or curvature that matches a shape and/or curvature of a surface of the structure to be inspected.
 10. A method for evaluating a bond, comprising: placing an open portion of a first vessel against a bonded structure being inspected; pulling a vacuum between an outer surface of the first vessel and an inner surface of a second vessel that encloses the first vessel, wherein pulling the vacuum seals the first vessel to the bonded structure; filling the first vessel with a liquid, wherein the liquid contacts a surface of the bonded structure to be inspected at the open portion; initiating a spark discharge in the liquid to form a plasma that generates a compression wave in the liquid, wherein the compression wave propagates from the liquid into the bonded structure through the open portion to apply a force to a bond in the bonded structure; and inspecting the bond in the bonded structure.
 11. The method of claim 10, wherein the bond in the bonded structure comprises a metal-to-composite adhesive bond or a composite-to-composite adhesive bond.
 12. The method of claim 10, wherein pulling the vacuum between the outer surface of the first vessel and the inner surface of a second vessel comprises compressing seals disposed between the first vessel and the bonded structure and compressing seals disposed between the second vessel and the bonded structure.
 13. The method of claim 10, wherein filling the first vessel with a liquid comprises filling the first vessel with water or oil.
 14. The method of claim 10, wherein filling the first vessel with the liquid comprises introducing a pressure of up to about 100 psi in the first vessel.
 15. The method of claim 10, wherein initiating the spark discharge in the liquid comprises supplying about 40 kV to about 60 kV to a pair of electrodes disposed in the first vessel.
 16. The method of claim 10, wherein initiating the spark discharge in the liquid to form the plasma generates a compression wave in the liquid having a pulse width of about 100 ns to about 300 ns.
 17. The method of claim 10, wherein initiating a spark discharge in the liquid comprises providing an electrical pulse from a bank of capacitors to a spark plug.
 18. The method of claim 10, wherein the force applied to the bond by the compression wave is from about 30% to about 70% of a force required to break the bond.
 19. The method of claim 10, further comprising applying another force to the bond by a reflected compression wave.
 20. A system for evaluating a bond comprising: a first vessel comprising, one or more sidewalls and an endwall, a liquid port configured to connect to a source to fill the first vessel with a liquid, and an open portion configured to be placed against a bonded structure to be inspected; a second vessel surrounding the open portion of the first vessel, comprising a vacuum port configured to connect to a vacuum system to pull a vacuum in a space between an outer surface of the first vessel and an inner surface of the second vessel when the open portion of the first vessel and an open portion of the second vessel are adjacent to the bonded structure to be inspected; and a pair of electrodes disposed within the first vessel and positioned to generate a compression wave in the liquid within the first vessel directed towards the bonded structure to be inspected. 